1. Field of Invention
The invention relates to the use of amorphous carbon-hydrogen (a-C:H) layers as hardmask material with tunable etch resistivity and use of these hardmasks in reactive ion etching (RIE) processes.
2. Description of the Prior Art
Because of the increase in complexity and reduction in the minimum feature sizes of circuit elements when fabricating microelectronic devices, contemporary exposure tools and highly sensitive photoresists are utilized to generate micrometer and sub micrometer pattern sizes. Further, because wet etching during fabrication causes several critical problems in pattern transfer of fine geometries, reactive ion etching (RIE) [which is characterized by low pressures and high-ion-bombardment energies] is used as it has several advantages over wet chemical etching. The advantages are: adhesion problems are not critical with plasma etching techniques; dry etching operations require small amounts of chemicals; and plasma-etching can be fully automated. Finally, RIE is especially useful because of its ability to etch anisotropically at low temperatures.
With decreasing feature size, the depth of focus of lithography also decreases and leads to reduced mass thickness, and this soft mass thickness is no longer sufficient to grant an adequate manufacturable process window for etch processes. For this reason, a lot of hardmask processes are becoming the state of the art. Nevertheless, many hardmask processes are dominated by chemical etching which is problematic, in that, i.e. in the case of Al RIE or Si etch, redeposited photoresist can be essential to provide sidewall passivation and thereby enable obtaining an anisotropic profile. Contemporarily, when using the state of the art hardmask processes, this sidewall protection mechanism is no longer available and this makes critical dimension (CD) control very difficult.
A fast deposition of a-C:H using an expanding thermal plasma beam is disclosed in van de Sanden et al., Plasma Science, 1993. IEEE Conference Recordxe2x80x94Abstracts., 1993 IEEE International Conference on pages(s): 225 Jun. 7-9, 1993. This fast deposition method utilizes a thermal plasma which expands into a vacuum vessel to deposit a-C:Hxe2x80x94wherein the deposited layer is produced by mixing methane or acetylene to argon carrier plasma.
The application of diamond-like carbon films to the integrated circuit fabrication process is disclosed by Komatsu et al. in Diamond-And Related Materials 8 (1999) 2018-2021. The amorphous diamond-like carbon (DLC) films have been developed as resist materials for lithography and as hard coatings, and the etching properties of these DLC films were obtained by first using a parallel-plate rf plasma glow discharge, methane gas decomposed for deposition of the DLC film on a substrate, and the use of oxygen to etch the film. The etching rate of the DLC films increase with decreased oxygen pressure. At high pressure, isotropic etching by neutral radicals occurred, since the shape of the etched edge was not vertical. The top and bottom edges coincided vertically at low pressure because of high bias voltage.
Sidewall surface chemistry in directional etching processes is disclosed by Oehrlein et al. in Materials Science and Engineering, 24 (1998) 153-183. This publication reviews the approaches used for silicon, aluminum, SiO2 and polymeric materials to suppress etching reactions at microstructure sidewalls, where the prerequisite of successful microstructure fabrication in electronic materials using plasma-base etching entails the ability to maximize the ratio of ion-enhanced etching reactions relative to spontaneous etching reactions, in view of the fact that, to produce vertical etching profiles, the rate of etching reaction in line-of-sight of the plasma has to be large, whereas the lateral etching rate should vanish.
U.S. Pat. No. 6,316,167 B1 discloses tunable vapor deposited materials as antireflective coatings, hardmask, and as combined antireflective coating/hardmask. The lithographic structure comprises a plurality of layers at least one of which is an RCHX layer which comprises a material having the structural formula R:C:H:X, wherein R is selected from the group consisting of Si, Ge, B, Sn, Fe, Ti and combinations thereof and wherein X is not present or is selected from the group consisting of one or more of O, N, S, and F and a layer of an energy active material.
There is a need, especially in the case of processes dominated by chemical etchings (i.e. Al RIE) to provide good selectivity of a potential hardmask material that is sufficient for a controllable process, because the selectivity of hardmask materials to the material that has to be etched is comparatively high, and therefore, the amount of redeposited materials is not sufficient to reliably protect the sidewalls of the growing features in the etch process.
An objective of the present invention is to provide an amorphous carbon-hydrogen (a-C:H) layer as a hardmask material with tunable etch resistivity for RIE processes dominated by chemical etching.